Currently, when it is necessary to completely remove a disc from between adjacent vertebrae, the conventional procedure is to fuse the adjacent vertebrae together. More recently, there have been important developments in the field of disc replacement, namely disc arthroplasty, which involves the insertion of an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae. This then allows limited universal movement of the adjacent vertebrae with respect to each other.
Some instruments have been developed to date for preparing an intervertebral space for receiving an artificial disc implant. These include a set of different sizes of trial implants, different ones of which are inserted into a cleaned out intervertebral space until the correct size trial implant has been determined, thereby determining the size of the actual disc implant to be permanently inserted. The trial implant may have a fixed stop member in the form of a pin fixed to the rear end of the trial implant and extending vertically up and down for limiting movement of the trial implant into the intervertebral space.
Some disc implants have a raised keel on each endplate which requires that a cutout be formed in the vertebrae adjacent the intervertebral space for receiving these raised keels. One known arrangement for forming these cutouts is with a chisel which can be mounted to move along slots in the top and bottom of the selected trial implant as the chisel cuts into the adjacent vertebrae to form the cutouts.
Besides a slot made by chiseling, drilling or milling can also be used, and combinations of these procedures are possible as well. However, where a chisel cut is made using a chisel and a mallet, quite high forces are applied in direction of the cut. With drilling, lesser forces are applied, but the drill can slip of or bend during drilling. With milling, a precise cut is made without high forces, but the milling tool needs to have a certain diameter, because otherwise it will break during milling and consequently milling is not always possible where a long narrow cut is required. Thus, a procedure used to perform narrow cuts without applying high forces is desirable. Exemplary of such prior art devices and methods are those disclosed in USPA 2004-0215198 (Marnay et al.) and USPA 2006-0064100 (Bertagnoli et al.), which are hereby incorporated by reference.
One known artificial disc implant is shown in Published Application No. WO 01/01893, published Jan. 11, 2001; and instruments for inserting same are shown in U.S. Pat. No. 7,118,580 (Beyersdorff—or Published Application No. WO 01/19295) and USPA 2004-0215198 (Marnay—or Published Application No. WO 04/098380). These references are also hereby incorporated by reference.
While these known instruments and methods represent a substantial improvement in the art, there exists a continuing need for improvements in the field of instruments and methods for preparing an intervertebral space for receiving an artificial intervertebral disc implant.